Add global comment/pings override switch

Description

One of the things we see a lot on the wordpress support forum is user confusion with regards to disabling/enabling comments.

Often, people will, in an attempt to stop spam, immediately try to disable comments. They are understandably confused when disabling: "Allow link notifications..." and "Allow people to post comments..." on the Options->Discussion page has no actual effect. As we know, these only set the default settings for comments and pings, flipping them off does not change the "on" status of comments and pings for all the existing posts.

I propose adding a global override switch labeled something like "Disable all comment functionality" and maybe a little explanation along with it. This will set a flag/option that the comments/pingbacks/trackbacks functions will check and be a single global on/off switch. This will allow people to do an instant kill of all the input functionality and restore it later, without changing any post settings or anything like that.

It would be useful to eliminate the user confusion here, but it would also be useful for short term attacks on sites, where lots of spam or comment posting or what have you is coming in. A simple way to disable all commenting would be useful.